There are many daily buses from Dar es Salaam. Driving time is seven to eight hours with a stop in Morogoro.Shabiby buses leave from Ubungo and are the most luxury buses at this moment. Around 11AM busses from Dar and from Dodoma which is air conditioned and has more leg space.
There are buses to and from Arusha via Kondoa to the north. The road is not paved, and can be bad in the rainy season. The highway is known as the Great Northern Highway. Travel time is often in excess of 12 hours, and breakdowns are common. The best plan would be to use Kondoa as an intermediate overnight point and continue north or south the next day.
There are also buses to and from Iringa. Travel time is about six hours on a winding gravel road of varying quality. The road passes right over the Mtera Dam which is worth a look.
Dodoma is situated on the Central Railway Line which goes from Dar Es Salaam to Mwanza or Kigoma. However, the train currently March 2010 only operates between Dar Es Salaam and Dodoma due to damages near Tabora. If you are in a hurry the better choice is by bus. If the train service is running again and you are heading west, train is better, especially in the rainy season.
Air Zara flies daily with the exception of Saturday between Dodoma and Dar es Salam for 250.000 TSH on Monday and Thursday, also to Mbeya. Tickets can be bought at the New Dodoma Hotel. Mission Aviation Fellowships' MAF small planes fly throughout the country; they have a regular shuttle between Dodoma and Arusha every Monday and also fly regularly to Nairobi and Mbeya. It is also possible to join other flights, for more information see their website and subscribe to their Joiner List.